Original code and complement code conversion

The complement of a positive number is its original code, except that the sign bit is always 0, that is:

真值：1， 原码：00000001B， 补码：00000001B

The complement of a negative number is the complement of its absolute value, invert each bit and add 1:

真值：-1， 绝对值：1， 绝对值补码：00000001B， 
补码=各位取反加 1 ：11111110B+1B = 11111111B = ffH

The complement of the negative number is converted to the true value by inverting the complement and adding 1, and then adding a '-' minus sign:

真值：-1， 补码： 11111111B，各位取反加 1 添负号：-00000001B = -1